如何列出从Ruby中的类创建的所有对象? [英] How do I list all objects created from a class in Ruby?

问题描述

在Ruby中，类是否可以通过某种方式知道它存在多少实例，并且可以列出它们?

Is there any way in Ruby for a class to know how many instances of it exist and can it list them?

这是一个示例类:

class Project

  attr_accessor :name, :tasks

  def initialize(options)
    @name = options[:name]
    @tasks = options[:tasks]
  end

  def self.all
    # return listing of project objects
  end

    def self.count
          # return a count of existing projects
    end


end

现在，我创建此类的项目对象:

Now I create project objects of this class:

options1 = {
  name: 'Building house',
  priority: 2,
  tasks: []
}

options2 = {
  name: 'Getting a loan from the Bank',
  priority: 3,
  tasks: []
}

@project1 = Project.new(options1)
@project2 = Project.new(options2)

我想要的是拥有类方法，如Project.all和Project.count，以返回当前项目的列表和计数.

What I would like is to have class methods like Project.all and Project.count to return a listing and count of current projects.

我该怎么做?

推荐答案

您可以使用ObjectSpace模块执行此操作，特别是

You can use the ObjectSpace module to do this, specifically the each_object method.

ObjectSpace.each_object(Project).count

为完整起见，这是您在课堂上使用它的方式(向锯齿倾斜)

For completeness, here's how you would use that in your class (hat tip to sawa)

class Project
  # ...

  def self.all
    ObjectSpace.each_object(self).to_a
  end

  def self.count
    all.count
  end
end

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